Low ampere circuit breaker with indirectly heated thermal element



0C1. 29, F. E MYERS LOW AMPERE CIRCUIT BREAKER WITH INDIRECTLY HEATED THERMAL ELEMENT Filed June 10, 1966 3 Sheets-Sheet 1 INVENTOR. 622/1 4? fl/Kczes Oct. 29, 1968 F. E. MYERS 3, 08,606 LOW AMPERE CIRCUIT BREAKER WITH INDIRECTLY HEATED THERMAL ELEMENT Filed June 10, 1966 3 Sheets-Sheet 2 INVENTOR. /Z2/x Mrces BY Oct. 29, 1968 F. E. MYERS 3,408,606 LOW AMPEREJ CIRCUIT BREAKER WITH INDIRECTLY HEATED TRERMAL- ELEMENT Filed June 10, 1966 3 Sheets$heet 5 INVENTOR. *22/4 4? es BY Q/ZeaZa g Qaag 125 {afa .5M

United States Patent ABSTRACT OF THE DISCLOSURE A circuit breaker construction intended for low ampere applications, typically below 4 amperes, which includes the b WITH INDI- My invention relates, in general, to circuit breaker des intended for low ampere applications,

operation.

My US. Patent No. 2,996,589, issued Aug. 15, 1961, entitled Pivoted Bimetal and assigned to the'assignee of the instant invention, shows a presently available circuit breaker device for home and light industrial use which has achieved wide-scale utilization liable and eflicient in operation, and may be rapidly and economically manufactured and calibrated.

The overload responsive trip means of such circuit breaker devices includes a thermally responsive elonsame degree of reliability, of manufacture and calibration provided by the higher rating commercial type circuit breakers.

3,408,606 Patented Oct. 29, 1968 ers having a nominal load rating of 1, 2, 3 and 4 amperes, with modification of the overload tripping characteristic being achieved by varying the heater means.

In order to provide tripping, inter-pole tripping, in a particularly convenient manner.

In addition to the thermally responsive moderate overload trip, an instantaneous,

commercial type circult breaker previously limited to higher ratings.

A further object of my invention breaker device lowing descriptions and drawings, in which:

F 1 is a side elevation view of a circuit breaker constructed in accordance with my invention, with the cover removed, and shown in the ON condition.

FIG. 2 is a side elevation view of the thermally rea consideration of the folcontact arm and load terminal sub-as- FIG. 1.

sponsive element, sembly portion of the circuit breaker shown in FIG. 3 is an end view of FIG. 2.

FIG. 4 is a modification of the circuit breaker shown in FIG. 1, to include an instantaneous magnetically actuated trip, in addition to the bimetallic thermally actuated trip shown therein, as well as an inter-pole trip member.

FIG. 5 corresponds essentially to FIG. 4, but shows a modified arrangement for interconnecting the inter-pole trip member to the individual circuit breaker trip means.

Circuit breaker ishoused within a molded insulative casing 11, which includes a plurality of recesses for receiving and locating the various operating components thereof. The open side of casing 11 is capped by a removable cover (not shown), which is also constructed of a molded insulating material, and which is secured to base 11 by rivets 21, which pass through aligned apertures of the base and cover. Located within housing 11 is a stationary contact 22 which is electrically connected via conductor member 24 to line terminal 26, which is illustratively shown as a screw type terminal. It should, however, be understood that a plug-in type terminal may be substituted therefor in the well-known conventional manner. Cooperating with stationary contact 22 is a movable contact 26, which is mounted at the lower end of movable contact arm 27. Parallel plate slotted arc extinguishing means 99 may be provided within recesses 101 of the circuit breaker molded housing. The upper bifurcated end of contact arm 27 abuts a suitable pivot formation in internally extended portion 28 of manual operating member 15. Manual operating member is pivoted about protrusion 14 thereof, which is entered into suitable recesses of the base 11 and cover, and includes an outwardly extending portion 16 to provide a handle operator for manually moving the circuit breaker between its manual OFF and manual ON positions, in the manner more fully discussed in my aforementioned U.S. Patent No. 2,996,589.

The operating mechanism for bringing about the enagement and disengagement of the cooperating contacts 22, 26 further comprises a latchable cradle 31, which is pivotally mounted at one end thereof to base protrusion 32, and forms a latch tip 34 at its opposite end. One end of an operating spring 33 is tied to cradle 31 at aperture 29 intermediate the ends thereof, while the other end 0 spring 33 is tied to contact arm 27 at aperture 29'. Operating spring 33 is always in tension, thereby urging contact arm 27 upward into engagement with its pivotal mounting to manual operating member 15.

In the ON position of the circuit breaker, as shown in FIG. 1, the operating spring is in over-center relationship to the left relative to the pivotal mounting of contact arm 27, and serves to urge the movable contact 26 into firm engagement with stationary contact 22. The latch tip 34 of the latchable cradle 31 seats upon latch means 35 carried by the lower end of an elongated thermally responsive element 36, which may typically be of the bimetallic variety. Latch means 35 is shown secured to the thermal element 36 by a rivet member 37, extending through an aperture at the lower end thereof, with an insulative plate 39 preferably also being provided. A bearing pin 41 is suitably secured to the upper end of the element 36, as by welding, and enters suitable circular recesses of the circuit breaker base and cover for pivotally mounting the bimetal element 36 thereto.

Thermally responsive element 36 is biased in a clockwise direction by spring 70, which is disposed in recess 72 of base 11, with one end of spring 70 abutting the internal wall of the recess and the other end of spring 70 abutting a portion of elongated thermal element 36 above its pivotal mounting 41. Accurate calibration of thermal element 36 is set by adjusting screw 74, which extends through an opening 79 in base 11 and is received by nut 76, disposed in a suitable recess 81 of base 11. The end 78 of screw 74 opposite its head abuts one leg of tensioning member 80, thereby forcing tensioning member against thermal element 36 to calibratingly move the thermal element about its pivot 41.

In order to provide appropriate overload responsive movement of elongated thermally responsive element 36 at the appreciably lower magnitudes to which the instant invention is directed, I provide an indirect heater means 50 in the form of a plurality of windings, coiled about an intermediate longitudinal portion of the elongated thermal element 36, and suitably insulated therefrom, such as by insulative sleeve 52, intermediate the surface of the thermal element 36 and the individual windings or the heater means 50. One end 54 of the heater means is connected via conductor 56 to braid 58, which in turn is connected to the movable contact arm 27. The other end 57 of the heater means is connected to braid member 60, which in turn is connected to the load terminal 62.

Thus, the current carrying path through circuit breaker 10 beginning at the line side thereof proceeds from line terminal 26, through conductive member 24, to stationary contact 22, to complementary moving contact 26, contact arm 27, and braid 58, through conductor 56 to end 54 of the heater means, serially through the heater means 50 to its opposed end 57, and through conductor braid 60 to load terminal 62. Thus, it is seen that the heater means 50 is in the series path of current flow through the circuit breaker 10, with thermally responsive element 36 being electrically insulated therefrom.

When circuit breaker 10 is subjected to a moderate overload condition, in accordance with the prescribed inverse time current characteristics thereof, the heat generated with heater 50 will deflectively move the latched end of elongated thermal element 36 in the direction of arrow 100, so as to defeat the latched engagement of cradle latch tip 34 and latch means 35. This will permit cradle 31 to rotate clockwise about its pivot 32, so as to change the over-center relationship of operating spring 33 to the right with respect to the pivotally mounted end of contact arm 27 and impart a quick-break movement of cooperating contacts 22, 26 to the TRIP condition.

Heater means 50 is designed in conjunction with the characteristics of thermal element 36, such that sufficient deflective movement will be imparted thereto to satisfy the prescribed inverse-time tripping characteristics, which may typically be a maximum of two minutes at 200% of rated current and one hour at 135% of rated current. Further, in order to provide sufficiently active operation, thermal element 36 must be relatively thin, and hence the pivotal mounting 41 thereof rather than a fixed or rigid mounting of the bimetal end serves to prevent permanent deflection of its weak cross-section during relatching of the circuit breaker.

In accordance with a particularly advantageous feature of my invention, the thermal element 36 of individually rated circuit breakers in the range of 1-4 amperes may be made identical with the differing ratings being achieved by suitable modification of heater means 50. This may be accomplished by changing the number of turns and/or gauge of the wire, to progressively increase the resistance of the heater at the lower ampere rating capacities of the breaker. Alternatively, the heater construction may remain unchanged, with different thermal elements being used for the different circuit breaker ratings.

Reference is now made to FIG. 4, which shows the added provision of an instantaneous, or magnetically actuated, trip, which includes a magnetic member 90, mounted at one end thereof, within suitable recesses 92, 94 of the circuit breaker housing 11, and the other end 96 thereof being closely adjacent the pivot end of the thermal element 36. If desired, an armature member (not shown) may be secured to the lower end of the thermal element. Thus, magnetic flux generated by heater means 50 extends across the V-shaped air gap intermediate magnetic member and the lower end of thermal element 36. Upon the occurrence of a severe fault condition, the free end of thermal element 36 is rotated towards mag- 3,408,606 6 netic member 90, closing the air gap, and thereby desive privilege or property is claimed are defined as folfeating the latched engagement of cradle latch tip 34 lows: and latch tip 35 so as to provide instantaneous tripping 1. A circuit breaker comprising: of the circuit breaker. a housing containing a stationary contact, a cooperating The modifications of the circuit breaker shown in FIG. movable contact and an operating mechanism for 4 include provisions for inter-pole tripping, in the genmoving said contacts between contact engaged and eral manner shown in my above-mentioned U.S. Patent contact disengaged conditions;

No. 2,996,589. A trip member 102 is pivotally mounted said operating mechanism including a manual operating to the common pivot 41 of elongated bimetallic element member pivotally mounted to said housing, and hav- 36. Trip member 102 includes a rectangular aperture 104, ing a first portion projecting outward of said housing, W ich receives elongated tie bar 106, extending outside 10 and a second portion internal of said housing said of the circuit breaker housing for connecting trip memfirst portion providing a handle operator for manuber 102 to the trip members of additional similarly conally movlng said operating mechanism between structed circuit breakers ad acent thereto, with reference manual ON and manual OFF positions being made to the aforementioned US. Patent No. 2,996,- a Contact arrn htrvlng a first and second end sald first 589, for the details of this inter-connection, A roller end carrying said movable contact and said second member 108 carried by cradle 31 engages trip member end pivotally mounted to said second portion of the 102 upon operation of cradle 31 between its latched, cirmanual Operating member;

cuit breaker ON position to the TRIP position. Engage a latchable cradle ng a fir and second said ment of trip member 102 by roller 108 forces trip memfirst end pivotally mounted to said housing and said her 102 counter-clockwise about pivot 41. This countersecond end forming alatch p;

clockwise movement is sufficient to engage upwardly exan Operating spring having a first and sect nd find, said tending thermally insulative member 110, secured to the first end connected to an intermediate Portion of said elongated th rmal l nt 36, so as t move it i h latchable cradle and said second end connected to an trip direction of arrow 100 a suflicient amount, to defeat intermediate Portion of said Contact e latched engagement of members 34, 35 That is an overload responsive trip means having a current should circuit breaker unit 10 move to its tripped conrating of not more than four p and lntihldlno dition, it will move member 102 counter-clockwise, with an elongated thermally responslve slemfint haV1n a such movement being transmitted via tie bar 106 to first and second end Plvot means at sald e n e the trip members of the adjacently aligned similar cirfor pivotally mounting said thermally responsive cuit breakers trip, the trip member 102 of the circuit ment to sard housing and latch Insans flamed at Conversely, should one of such ad acently aligned cir- 831d Second end for latchlng emagsrnent With stilld cuit breakers trip, the trip member 102 of the circuit .latchahle CradIeIatChtrP; breaker shown will be moved counter-clockwise to en- 531d ctrchit breaker ON Position corresponding to said gage member 110 and thereby move circuit breaker 10 latch p being in engagement With Said latch means, t it t i o diti and said operating spring being in overcenter relat i t d th t th h t i di 59 are advantionship relative to the pivotal mounting of said contageously limited to an intermediate portion along the tact arm for hrgln" sald movable Contact Into length of thermal element 36 intermediate pivotal mountgagemeht Wlth Sald statlonary Contact, ing 41 and displaced from latch means 35. Should the redetermined heating of said thermally responsive elewindings be placed close to the latch, it mi ht interfere Iheht deflectively moving the second end thereof In a with its operation. Further, by not having the heater dlfection to defeat the latching engagement h coils 50 at the lowermost end of the element 36, an sald cradle latch such that said Operating spring armature member may be convemenfly addmi moves said cradle in a direction to alter the over- Reference i made to FIG, 5 which Shows a modifica 45 center relationship of said operating spring relative ti f h manner In hi trip member 102 engages to said contact arm and rapidly moves said movable elongated bimetallic element 36 Upwardly extending Contact out of engagement Wlth said stahohary member 110 secured to the bimetallic element of FIG tact to the clrchlt breaker TRIP Conthtlon 4 h now b replaced with an extension of trip a heater means for said thermally responsive element member 102, d serves h same f ti of moving in the circuit path of current flow through said cirlatch means 35 in the direction of arrow 100 upon the ,cult breaker; counter-clockwise movement of trip means 102. In both sald heater means including a plurality Of windings the embodiments of FIGS. 4 and 5, I advantageously wrahped about said thermally responsive men avoid having trip member 102 directly contact heater 50. longltudinany Positioned intermediate Said Pivot If such contact were permitted, member 102 might blister t and latch means; or swell from the heat of the heater coils, adversely insulating means for electrically insulating said therfecting the operation of theintemade trip mally respons ve element from the current flow It is therefore seen that my invention enables the conthrough stud clrcult break? a heater means;

struction of a circuit breaker device for low current magnitude, in the order of 14 amperes, which has the conditions.

breaker devices previously limited to appreciably higher 2. A circuit breaker as Set forth in Claim current magnitudes Further, it is seen that I achieve said trip means operatively constructed move sald these advantages y a relatlvely shnple rnodlficahon of circuit breaker to the TRIP condition responsive to such prior art devices, which utilize a maximum of the th d r t heating of said thermally responsive ele- PrsVlOns components and does not require y Its-Work ment upon the occurrence of an overload condition of the housing. satisfying predetermined inverse-time characteristics Although in the foregoing, my invention has been dein excess of the normal load ratin scribed in con unction with preferred embodiments many 3, A i i b k as t forth i l i 1;

variations and modifications Wlll now become apparent said trip means operatively constructed to move said to those skilled in the art and I prefer, therefore, that circuit breaker to the TRIP condition responsiv to the instant invention be limited not by the disclosure the indirect heating of said thermally responsive contained herein but only by the appended claims. element upon the occurrence of a moderate overload The embodiments of the invention in which an exclucondition satisfying predetermined inverse-time characteristics in excess of the normal load rating; of an overload in any of the connected circuit said trip means further including an instantaneous, breakers will move the trip members of all the cirmagnetically actuated trip, said instantaneous trip cuit breakers to effect simultaneous tripping thereof. having a magnetic member including a first and sec- 5. A circuit breaker as set forth in claim 2, further ond end, said first end positioned closely adjacent including: said thermall responsive element first end, and said a trip member movable by said latchable cradle upon magnet second end spaced from said thermally rethe movement thereof from the circuit breaker ON sponsive element second end to define therewith a condition to the circuit breaker TRIP condition, said V-shaped air gap having an apex at said first ends trip member when moved by said latchable cradle and open at said second ends; 10 engaging a portion of said trip means, which is said housing including seating means for said magnet carried by said thermally responsive element and is second end, such that upon the establishment of a thermally insulated from said heater means, means sufiicient flux path across said air gap, the second connected to said trip member and extending outend of said thermally responsive element moves toside of said housing for connecting said trip member wards said magnet second end to close the V, with to the trip member of at least one additional similarsuch movement serving to defeat the latching enly constructed circuit breaker, such that the occurgagement of said latch means and said cradle latch rence of an overload in any of the connected circuit tip. breakers will move the trip members of all the cir- 4. A circuit breaker as set forth in claim 1, further cuit breakers to eifect simultaneous tripping thereof. including: 6. A circuit breaker as set forth in claim 1:

a trip member movable by said latchable cradle upon said thermally responsive element being a bimetal.

the movement thereof from the circuit breaker ON condition to the circuit breaker TRIP condition, said References Cited trip member when moved by said latchable cradle NIT STATES PATENTS engaging a portion of said trip means, which is carried by said thermally responsive element and is 20 2215788 9/1940 Hamflton et a1 200-416 thermally insulated from said heater means means 2952757 9/1960 Enenberger 200-116 2,996,589 8/1961 Myers 200-416 connected to said trip member and extending outside of said housing for connecting said trip member to BERNARD A GILHEANY Primary Examine, the trip member of at least one additional similarly constructed circuit breaker, such that the occurrence COHRS Assistant Exammer' 

